Biodiesel is produced by transesterification of oils with short-chain alcohols or by the esterification of fatty acids. The transesterification reaction consists of transforming triglycerides into fatty acid alkyl esters in the presence of a short chain alcohol, such as methanol or ethanol, and a catalyst, such as an alkali, with glycerol as a by-product.
Biodiesel as a fuel is attracting increasing attention worldwide as a direct replacement for diesel in vehicle engines or, more commonly, as a blending component for diesel (Judd, 2002). The majority of biodiesel today is produced by alkali-catalyzed transesterification of oil or fat with methanol, in the presence of an alkali catalyst which results in a relatively short reaction time (Vasudevan and Briggs, 2008).
Waste vegetable oils and animal fats (tallow) are sources of oil or fat that may be used in the preparation of biodiesel.
Sims (1983) noted the availability of substantial quantities of tallow in New Zealand as an opportunity for local biodiesel production.
In 2002, some 150,000 tonnes per annum of tallow was produced in New Zealand and some 2 million tonnes per annum of diesel was used (Judd, 2002). At these production and use rates a 6% biodiesel/mineral diesel blend could be produced satisfying local demand using locally sourced tallow.
Where the demands for biodiesel production are higher, biodiesel is most commonly prepared by a continuous, as opposed to batch, reaction process. Plant capacities in excess of 100,000 tonnes per annum are known.
Economic justification for the commissioning and operation of Plant with these capacities does not exist while the local demand for biodiesel production is relatively low. Economic justification for the commissioning and operation of plant with these capabilities does not exist when the sources of oil or fat are distributed across remote areas.
The preparation of biodiesel by a batch reaction process may be appropriate while the local demand for biodiesel production is relatively low or the sources of oil or fat are distributed across remote areas. In these circumstances plant that is cost effective to establish and operate is required.
The preparation of biodiesel from waste oil or animal fats (tallow) requires pre-treatment of the source of oil or fat to remove excess entrained water and/or free fatty acids that would otherwise interact with the alkali catalyst to form soaps.
It is an object of the invention to provide a method of preparing biodiesel that is particularly suited for use in batch manufacturing processes using tallow as a source of fat.
It is an object of the invention to provide apparatus adapted for use in preparing biodiesel that is particularly suited for use in batch manufacturing processes using tallow as a source of fat.
These objects are to be read disjunctively with the object of to at least provide a useful choice.